The 20-year-old Masters rookie is tied with Bubba Watson, who lets a five-shot lead get away. But it's more than a two-man race.

AUGUSTA, Ga. — Adam Scott, the 2013 Masters champion, had already fulfilled his interview obligations behind the Augusta National clubhouse Saturday, his demands smaller than usual with a third-round 76 dropping him into 16th place and bursting the bubble of his repeat bid.

So the Masters spotlight quickly shifted within Scott's group, to a caddie of a 20-year-old Masters first-timer.

Michael Greller was the new encircled man, the on-course compass for Jordan Spieth, a wildly skilled Texas kid with eye-opening maturity and an unlikely emergence as the 54-hole Masters co-leader.

Greller was offering a pack of reporters his insight on an impressive day when Spieth emerged from the scoring cabin with a surprised grin.

"I've got to take a picture of this," Spieth joked.

Spieth probably should be taking a multitude of mental snapshots from his first Masters field trip.

Of the massive galleries that are falling in love with his skills and serenity.

Of the Saturday 70 he shot — four birdies, two bogeys — showing a surgeon's equanimity under elevating pressure.

Of the Sunday pairings that put him in the final round's final group, alongside 2012 green jacket winner Bubba Watson.

Spieth is gunning to become the youngest major winner in 83 years and the youngest winner of the Masters.

Still, Sunday at Augusta can be a piranha to even the most experienced competitors. So Spieth is a long way from a celebratory fireside chat with CBS' Jim Nantz in Butler Cabin.

But his surge to the lead was the most compelling highlight of a carnival Saturday that had the on-course leaderboards spinning faster than a Tilt-A-Whirl.

Watson, who led by five shots early in the day after making an eagle on the second hole, lost his putting feel and seemed to play with his nails dug into a cliff throughout the rest of the round, ultimately carding a two-over 74. But he never fully lost the lead and remains in prime position to win a second Masters, if he can just soothe his anxiety.

He and Spieth are five under par, one shot head of Matt Kuchar and Sweden's Jonas Blixt, while nine other players will start the final round under par.

Rickie Fowler carded one of Saturday's five rounds in the 60s, uncorking a six-birdie effort for a five-under 67 that has him tied for fifth. And the third round's biggest charge came from 50-year-old Spaniard Miguel Angel Jimenez, whose best-of-the-week 66 shot him from three over at the start of the day to three under and tied with Fowler after 54 holes.

Jimenez acknowledged the value of Augusta experience, Saturday being the 53rd competitive round he has completed here. But he also noted the psychological challenge of embracing the tension.

"I feel fantastic," Jimenez said. "I like the feeling of the knot in my stomach. I feel that thing since Monday when I got here. It doesn't disappear. I love that kind of pressure."

Spieth has seemed to love it too, for three days anyway.

The fast greens, the elite company, the magnitude of the Masters. None of that has rattled Spieth — yet. One last 18-hole test remains, alongside Watson, under an intense microscope and among a horde of other hungry competitors.

"I don't think I've ever had a round where I've been nervous on every single swing, shot and putt," Spieth said. "I'm sure that will happen [Sunday], but hopefully I can channel it positively."

"Look," Greller added. "We've got nothing to lose. If we don't win? OK. No one expected us to win. You kind of feel like the underdog. It's kind of nice."